Be cautious of OP or counter-pick champions
Many League of Legends players without a focused champion pool will gravitate towards popular, overpowered (OP) champions or champions known for countering their opponent. Abiding by this mindset could cost you, though.
Let’s elaborate. Choosing a champion that’s currently strong, perhaps overpowered, is not a bad decision in and of itself. What can be problematic is having no familiarity or skill with a champion, but picking it nonetheless because it’s hyper popular or a one used to high success in competitive play. There are few moments in this life where a champion will be genuinely freelo (read: free ELO). Typically, the seemingly “OP” champions require a deep understanding of their mechanics, or at least some practice.
In the same vein of thought, picking a champion known to “counter” your enemy can become an unnecessary handicap. Unless you’re familiar with the counterpick, you’re more likely to perform worse with an unfamiliar champion than you would with a practiced hero that may not dominate the matchup on paper. If you’re skilled enough, you can even play your best champions into an unfavorable matchup.